The importance of potential regions of amphiphilic secondary structure in determining the biological functions of peptide hormones will be determined. The natural peptides to be studied as examples include the serum calcium regulator calcitonin and peptides involved in behavior modification, epithelial ion transport, blood pressure regulation and other important effects, including calcitonin gene-related peptide, and the neuropeptide Y/peptide YY/pancreatic polypeptide family. In these cases, potential amphiphilic alpha helices will be the first structures studied in relation to a variety of possible roles, including determination of receptor binding affinity and specificity, participation in folded tertiary structures, and the control of pharmacokinetic behavior in vivo, including proteolytic degradation. Two approaches will be employed. An investigation will be initiated into the design of amphiphilic alpha-helical peptides that have conformational constraints involving cyclic structures or non-natural amino acids chosen to stabilize the helical conformation. In addition, the novel approach of designing and synthesizing peptide models will be adopted, in which the potential for amphiphilic helix formation will be retained in an idealized form using amino acid sequences having minimal homology to the corresponding natural sequences. Functional importance will be determined by comparing the natural hormones to analogs containing the best helix-promoting constrained structures or the model sequences, in order to determine correlations between the analog design and their physicochemical and pharmacological properties. This approach will be extended to other potential conformational features of these hormones that, like the amphiphilic helices, are not readily identified in aqueous solutions but may be important in the functional environment. Ultimately, the arrangement of all structural segments of these peptide hormones on their receptor surfaces will be probed through the synthesis of conformationally constrained peptide analogs that may include idealized models of several conformational features such as alpha helices, beta turns, collagen-like helices and flexible "random coil" structures, composed by both natural and non-natural amino acids. These studies should allow the rational design of potent and specific agonists and antagonists with predictable pharmacokinetic behaviors that might be useful as pharmacological tools or even therapeutic agents. The lessons learned should be widely applicable to the engineering of proteins in general.